I. Field of the Invention
This invention relates generally to computer controls for machines. In particular, this invention relates to computer controls for injection molding machines.
II. Description of the Prior Art
It is known from U.S. Pat. No. 4,486,830 to provide a programmable logic controller (PLC) executing high level language programs by means of interpreter routines. The disclosure of this reference describes programming of cycles defined by blocks providing logical and mathematical expressions relating input and output variables associated with bit and word data representing, respectively, device conditions and parameter values.
It is known from U.S. Pat. No. 4,745,541 to provide an injection molding machine control wherein a PLC is combined with a programmable process control module for effecting closed loop control over machine mechanisms. In this reference, the programmable process control is connected to the PLC via the PLC system bus. Further, it is known from this reference to provide event detectors to continuously monitor selected analogue input signals representing controlled parameters and detect coincidence thereof with predetermined values to initiate execution of a programmed response. The event detectors of this reference were limited to use of selected analogue inputs, precluding the use of the event detectors in association with machine operations not represented by the analogue input signals.
It is known from, for example, the CAMAC injection molding machine control available from Cincinnati Milacron Inc., the assignee of the present invention, to provide event detector programming for a PLC wherein the event detectors operated with analogue inputs derived from analogue input interface modules connected to the PLC input/output (I/O) signal bus. Such controls were not supplied with programmable process control modules for effecting closed loop control but relied on analogue loop control interface modules.
The known injection molding machine controls described in the foregoing do not provide a control for injection molding machines wherein the programmability of a PLC is combined with a programmable servo control and event detectors responsive to events reflected by binary status signals and elapsed time signals as well as analogue input signals.